Don Klipstein wrote:

In article , Pete C. wrote:
HeyBub wrote:

Tony Hwang wrote:
Hi,
Nearby town of Banff installed LED street lights with solar panels.
Very cool looking light and it is cool running, no bugs get attracted
kep them clean. Cost a lot initially but for the long run, it's
winner. LED bulbs now are expensive but with time the price will come
down. I have a few small ones in the house, they use couple Watts per
bulb.

My city, Houston, is retrofitting its traffic signals with LEDs. They cost
more initially, but since the bulbs won't have to be replaced for, what,
fifty years, they should recoup the expense fairly soon.

I doubt the 50 yr thing since I've see LED signals failing. The good
thing is that they have a "soft" failure mode, losing a few strings of
LEDs rather than the whole thing at once like the old incandescent
signals. The power savings of the LED vs. the 300W incandescents they
replace becomes significant when multiplied by all the active signals in
a city.

300W is awfully high for a traffic signal incandescent. Look in a lamp
catalog by any of the "Big 3" makers and see what wattages "traffic signal
lamps" come in. I somehow think 116 watts is a popular one.

It's been a long time since I looked at them.


Now, major reasons why LEDs can do the same job with 12 watts or so (for
red and green): Mostly, because an incandescent with a red or green
filter in front of it has the filter remove about 2/3 of the light.
Meanwhile, LEDs normally specialize in producing light of a particular
color. (The usual white ones have blue-emitting chips and a phosphor that
absorbs some of the blue light and fluoresces out a broadband yellowish
light whose sectrum goes from mid-green to mid-red.)

Another reason why incandescent traffic signal lamps are easy to improve
upon in energy efficiency is because they are superlonglife vibration
resistant versions that have about 65% of the efficiency of "standard" 750
hour incandescents. LED units also have more carefully controlled
directivity patterns and less light is wasted by going where it does not
need to go.

A couple of the features that make LEDs good for signals that you point
out, and which also make them good for other warning type signals -
Tight emissions spectrum and directional output - are the reasons that
current LED technology is not appropriate for residential lighting use.
Residential lighting needs a much broader output spectrum and wide beam
pattern. When they get an LED with a "warm white" equivalent output
spectrum and a wide beam spread then they'll be on the way to
residential lighting applications. Price will still have to be brought
down a lot, but once the units are mass market acceptable production
scale should take care of price.